Medically reviewed by Kristin Hall, FNP
Written by Our Editorial Team
Last updated 3/19/2021
Depression is a common mental disorder. According to data from the 2017 National Survey on Drug Use and Health, more than 17 million adults in the United States experienced at least one major depressive episode during the previous year.
Like many other mood disorders, depression can vary in severity. While some people develop mild depression, others are affected by severe symptoms that can last for years.
In addition, the causes of depression are extremely complex and vary substantially by individual. Experts have identified a wide variety of factors that can combine and lead to depression, from your genetics to stressful life events, trauma and many others.
Below, we’ve provided more information about how depression develops, as well as the factors that may play a role in the process.
We’ve also talked about the different types of depression and the unique factors that can cause each one.
Finally, we’ve explained what you should do if you’re feeling depressed and want to take action to find help, treat your depression and improve your quality of life.
Depression is a complex mood disorder that often develops due to multiple causes, from changes in your life or traumatic experiences to factors related to your genetics.
You may have heard that depression is caused by certain aspects of brain chemistry that affect your brain. While brain chemistry does appear to play a role, there are a variety of biological — as well as social and environmental — factors can cause these issues to develop.
There are several types of depression. Many cases of depression are mild or moderate in severity, while others are described as major depression.
Other types of depression include seasonal affective disorder (SAD), atypical depression and others. These types of depression often have distinct causes.
No matter what the cause of your depression might be, depression is treatable. If you’re feeling depressed, you can talk to a healthcare provider to learn more about the options available to you.
Although depression is one of the most common, frequently treated mood disorders, experts still aren’t fully aware of what causes it to develop.
This is because unlike many other illnesses, which are caused by a specific pathogen or internal dysfunction, research into depression suggests that it can be caused by a variety of factors.
If you’ve researched about depression, you’ve likely heard that depression is linked to unusually low levels of certain neurotransmitters in your brain, such as serotonin.
Neurotransmitters are chemicals that transmit information between your neurons. Experts have currently identified more than 100 different neurotransmitters, many of which play essential roles in your brain and body’s functioning.
Currently, experts believe that several different neurotransmitters may be related to depression symptoms. These include:
Serotonin. This neurotransmitter helps to regulate your mood, appetite and sleep. It’s also involved in inhibiting pain. Research suggests that many people with depression have a reduced level of serotonin transmission in the brain.
Norepinephrine. Also known as noradrenaline, this neurotransmitter is responsible for increasing your blood pressure and constricting your blood vessels. It may also affect your level of motivation and feelings of reward.
Research suggests that norepinephrine plays a role in the development of depression symptoms, as well as certain anxiety disorders.
Dopamine. This neurotransmitter affects how you perceive reality and plays a key role in making you feel motivated. It’s released when you expect to be rewarded, making it an important part of your brain’s reward system.
Acetylcholine. This neurotransmitter improves your memory and plays a major role in learning. It’s involved in activating your muscles and allowing you to control and focus your attention on specific tasks.
Gamma-aminobutyric acid (GABA). This neurotransmitter works by inhibiting certain types of brain activity. Studies suggest that people with certain anxiety disorders and depression often have reduced levels of GABA.
Most medications for depression work by increasing levels of these neurotransmitters in order to reduce the severity of your depression symptoms and restore your mood.
Other factors related to your brain function, such as nerve circuit functioning, nerve cell growth and nerve cell connections, also play a role in depression.
Certain factors, such as major changes in your life or stress, can make you more vulnerable to depression. These are often referred to as depression risk factors.
People often become depressed when a combination of different factors all take a toll on their mood and quality of life.
For example, being diagnosed with a medical condition can result in financial hardship, stress, reduced social contact and other sudden life changes. This combination of factors can lead to an increased risk of developing depression.
Below, you can find more information about the most common risk factors for depression:
Depression often develops after one or several sudden changes in your life, especially if these changes lead to stress. Life changes that may trigger depression include:
Divorce or ending a relationship
Losing your job or another significant financial loss
Losing a family member, close friend or other loved one
Being diagnosed with a medical condition
Other unexpected, negative events
These events often have a negative effect on your mood. While these effects are short-lived for some people, others may experience a more persistent, severe low mood and depression when changes occur suddenly.
Trauma and abuse, especially when they occur during your childhood, may increase your risk of developing depression as an adult.
A range of traumatic events are associated with depression, as well as mental health conditions such as post-traumatic stress disorder (PTSD). Approximately half of all people with PTSD also suffer from major depressive disorder.
You may have a higher risk of developing depression and other mental health issues if you have experienced any of the following as a child:
Physical, sexual or emotional abuse
Physical or emotional neglect
Domestic violence, as a victim or witness
Other issues within your childhood household, such as substance abuse, parental separation or mental illness, may also increase your risk of developing mental health issues as an adult.
Chronic stress, a constant form of stress that usually occurs over a long period of time, is linked to a range of negative health issues, including anxiety and depression.
Common sources of chronic stress include relationship issues, financial issues or a demanding or dissatisfying work environment. These problems may develop over time, resulting in stress that worsens without any obvious path towards improvement.
Chronic illnesses and conditions that cause pain, especially when undiagnosed or unmanaged, can affect your mood and lead to depression.
These may include serious illnesses such as heart disease, diabetes or cancer, or illnesses that aren’t life-threatening but cause a significant reduction in your quality of life.
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Although there’s no single “depression gene,” research indicates that depression has a genetic component.
This means that if your parents or other family members have a history of depression, you may have an elevated risk of developing depression at some point in your life.
According to Stanford University School of Medicine, if you have a parent or sibling with major depression, your risk of developing depression is approximately two to three times higher than the average person’s.
Your risk is higher if you have a parent or sibling affected by recurrent depression -- a form of depression that occurs more than once -- that started early in their life.
You may have a higher risk of developing depression if you’re lonely and spend little or no time around other people.
Loneliness and depression often occur together. Not only can being lonely increase your risk of developing depression, but depression itself can often cause you to withdraw from your normal social life and spend less time around your close friends and family.
Substance abuse, whether it involves illicit drugs or substances such as alcohol, is often linked to depression.
People often use alcohol and other substances to self-medicate due to stress or after traumatic events. For example, someone with a demanding, stressful job may use alcohol to relax after a long, challenging day at work.
Over time, this may trigger or worsen depression. People who are already at risk of developing depression due to a major life change or other issue may be particularly at risk if they begin to abuse alcohol or other substances.
Certain medications, including numerous widely-used prescription drugs, are associated with an elevated risk of depression or depression symptoms.
Medications that may increase your risk of developing depression include certain antiviral drugs, cardiovascular medications, antidepressants, anticonvulsants, hormonal medications, oral acne medications, antipsychotics and smoking cessation agents.
Some other medications, such as opioid painkillers, may also contribute to an heightened risk of developing depression when misused or abused.
Finally, certain personality traits may make you more likely to develop depression or other mood disorders.
Research into the relationship between personality traits and depression has found that people who are depressed tend to display higher levels of neuroticism than the general population.
Neuroticism is defined as a tendency towards feelings such as self-doubt, irritation, anxiety and other negative emotions.
People with depression also typically score lower on personality traits such as extraversion and conscientiousness.
Most people associate the word “depression” with major depression, also referred to as major depressive disorder. This is a classic form of depression that can cause a persistent low, dark mood and other symptoms such as loss of energy, sleep issues and negative feelings.
In addition to major depression, there are several other forms of depression, some of which are caused by specific events or behaviors. These include:
Seasonal affective disorder (SAD). This type of depression typically develops during the fall and winter. Experts think that it may be caused by reduced exposure to sunlight, which may affect some people’s regulation of neurotransmitters such as serotonin.
This type of depression may also be linked to hormones such as melatonin, or vitamins such as vitamin D.
Persistent depressive disorder (dysthymia). This type of depression can last for long periods of time, including several years. It’s often less severe than major depression, but tends to cause similar symptoms.
Perinatal depression. This type of depression only occurs in women. It involves major and minor depressive episodes that can occur during pregnancy or in the first year after childbirth.
Premenstrual dysphoric disorder (PMDD). This is another type of depression that only occurs in women. It’s a severe form of premenstrual syndrome that occurs shortly before and during menstruation.
If you’re feeling depressed, it’s important to seek help. Depression is treatable, and talking to a licensed healthcare provider is an excellent first step towards overcoming your depression and working towards recovery.
Depression can be treated through medication, therapy and certain changes to your habits and lifestyle.Your healthcare provider may prescribe antidepressants to improve your mood and treat your depression symptoms.
Although antidepressants are effective, you may not notice their effects right away. It generally takes four to eight weeks before you’ll notice any improvement in your symptoms.
If suitable, your healthcare provider may recommend that you take part in psychotherapy, such as cognitive behavioral therapy (CBT) or interpersonal therapy (IPT).
These forms of therapy can teach you new methods of thinking and behavioral approaches to overcome depression. In certain cases, your healthcare provider may recommend other forms of therapy.
Finally, you may be able to improve your recovery from depression by making certain changes to your habits and lifestyle, such as:
Making an effort to exercise regularly and stay active
Setting short-term and long-term goals for yourself
Spending more time with friends, family and other people
Taking a long-term approach to improvement and recovery
Learning more about how depression occurs and how to avoid your triggers
Avoiding major life decisions until you’ve fully recovered from your depression
You can learn more about recovering from depression using medication, psychotherapy, lifestyle changes and more in our full guide to fighting depression.
Figuring out a singular “cause” for depression is a question that could never have a definitive, singular answer.
Because there’s no one singular “cause” of depression. The truth is, we’re just beginning to scratch the surface of learning why depression happens and what the best ways to treat it, are.
However, at a basic level, current research shows that a variety of factors may contribute to the changes in your brain that cause depression. These include major life changes, traumatic or abusive experiences, genetics and even certain personality traits.
And yes, individual brain chemistry plays a role, as well.
All of these things interact and combine to help shape what each individual’s relationship to depression is — including which symptoms of depression we experience and how severe our depressive symptoms are.
The real takeaway here is this: if you’re feeling depressed, it’s time to get help.
You can seek help by talking to a licensed healthcare provider to receive science-based, effective treatment.